Resistance pattern of Escherichia coli to levofloxacin in Iran: a narrative review

Fluoroquinolones (FQs) are widely used in the treatment of infections caused by Escherichia coli. FQs are broad spectrum antibiotics with high tissue penetration, and ease of use. Therefore, given the concerns existing about drug resistance, we aim to review the latest findings about resistance patterns to levofloxacin (LVX) along with other FQs in E. coli infections in different parts of Iran. Evidence shows that quinolones have been used in Iran for nearly 50 years, and that 0–65% of E. coli isolates show resistance to FQs. In the western parts of Iran, the highest rate of resistance to LVX (66.7%) has been reported among patients having urinary tract infections with E. coli isolates. Few studies and information exist on the antimicrobial resistance of E. coli to LVX in different geographical locations of Iran. However, the findings of various studies on this subject show that E. coli resistance to LVX is more in the western part of Iran than in central and southern regions, but it is similar among inpatients and outpatients. Therefore, it is reasonable advisable to limit the overuse, inappropriate prescription, and self-medication of LVX to prevent the induction of FQ-resistant strains. Accordingly, in order to obtain a clearer image of resistance to FQs, especially LVX in E. coli in Iran, more extensive investigations in different geographical locations and periods of time are required. In addition, antimicrobial stewardship would be helpful in this regard.


INTRODUCTION
Since the discovery and synthesis of antibiotics, life expectancy increased by 10 years; however, the World Health Organization (WHO) reported antibiotic resistance as a "major global threat" in 2014. According to a report by the UN-affiliated agency on 30 th April 2014, the world is entering the "post-antibiotic" period when simple infections that were curable for years would threaten individuals' life. The therapeutic effects of antibiotics are on the decline at an alarming and inevitable pace similar to the phenomenon of global warming (1,2). Antimicrobial resistance is greatly increasing among bacteria, and governments are spending large amounts of budgets to control it. It is necessary to use appropriate drugs for the treatment of infections (3,4). Escherichia coli is a bacterium in which antimicrobial resistance is increasingly high (5).
This microorganism is normally found in the gut microbiomes of mammals, birds, and fish (6,7). It provides some benefits to the hosts and plays an important role in the production of vitamins K and B12 both in hosts and biotechnology (7,8). However, E. coli is a major human pathogen that causes urinary tract infections (UTIs), enterocolitis, and septicemia in humans. Over 10 pathotypes of E. coli have been identified to date, and different pathotypes could cause similar diseases through various mechanisms (5,9).
Nalidixic acid was the first quinolone synthesized in 1962 (10). Due to its low oral absorption, limited antibacterial spectrum, high ability to bind to proteins, and low tolerability, nalidixic acid was restricted in treating bacterial infections. Thus, many fluoroquinolone analogs have been produced since the last decades (11). For example, norfloxacin, ciprofloxacin, and LVX were patented in 1987, 1980, and 1965, respectively (12,13).
LVX, the L-isomer of ofloxacin and one of the FQs, has been available since 1992 (14,15). Following the introduction of LVX and due to its strong effects on a wide range of Gram-positive and Gram-negative bacteria, many studies have been conducted to determine its benefits. However, researchers have reported that LVX overuse gradually induces the expression of resistant genes and leads to the emergence of resistant strains. Therefore, standardized discs containing LVX have been introduced, with the susceptibility patterns of different bacteria evaluated (16)(17)(18). LVX interferes with the DNA replication of the bacterium by inhibiting the activity of the DNA gyrase enzyme, thereby inhibiting the DNA synthesis of the bacterium. This characteristic prevents bacterial replication and produces bactericidal effects (19).
LVX is frequently prescribed to treat E. coli infections (14,(20)(21)(22). Because LVX is an effective therapeutic agent, it is prescribed by Iranian physicians for treating infections. It has some properties, including daily administration, high effectiveness, low cost, and minimum side effects (23). Several studies have been conducted on the antimicrobial resistance of E. coli to many antibiotics in Iran; however, few studies have been carried out to determine its resistance to LVX. Moreover, in a recent study on the limitation of the use of LVX, a reduction in the frequency of FQ-resistant E. coli species has been reported (24). Therefore, the present review aims to achieve a clearer image of the antimicrobial resistance of E. coli to LVX in Iran.
The mechanism of FQs' function. Quinolones with fluorine in their structure are called FQs, and LVX is a member of fluoroquinolone antibiotics. Fluorination enhances the effects of quinolones on both Gram-negative and Gram-positive bacteria and improves drug entry into the bacterial cells (25). According to the antimicrobial activity spectrum, quinolones are classified into four generations; the first generation includes cinoxacin, pefloxacin, and nalidixic acid; the second generation consists of ofloxacin, ciprofloxacin, enoxacin, lomefloxacin, and norfloxacin; the third generation is comprised of gemifloxacin, LVX, sparfloxacin, gatifloxacin, and moxifloxacin; and the fourth generation includes trovafloxacin and alatrofloxacin (10).
Quinolones have impacts on some facultative anaerobic Gram-negative bacilli, such as enterobacteriaceae. All compounds from the quinolone family have approximately a similar basic structure (4-aminoquinoline) and a mechanism of action (26). They inhibit DNA replication both selectively and reversibly, and stop sensitive bacteria by limiting the function of DNA gyrase and topoisomerase IV. DNA gyrase is a tetrameric enzyme with two subunits of A and B. These two subunits are encoded by gyrA and gyrB genes and play a central role in the unwinding and twisting processes of DNA. Similar to DNA gyrase, topoisomerase IV is a tetrameric enzyme with two subunits. These subunits are encoded by parE and parC genes and involved in separating two daughter chromosomes during the replication process. FQs commonly interfere with the GyrA subunit of DNA gyrase (27).
FQs serve as bactericidal drugs by inhibiting DNA replication and transcription. Both DNA strands are interconnected within the bacterial cell. For bacterial division, two strands of DNA should be separated from each other. To facilitate the separation of the strands, DNA gyrase helps strands get detached and rejoined (28,29). Thus, DNA gyrase is really essential for the survival and proliferation of bacteria. Most eukaryotic cells, especially in humans, lack this enzyme. Therefore, it could be considered an attractive target for antibacterial compounds, especially quinolones (30).
lvx's antimicrobial activity. LVX is most often used in treating patients suffering from several disorders, such as arthritis and skin infections, as well as disorders in the lungs, airways, sinuses, bones, urethra, kidneys, and prostate (31). It is reactive against a broad spectrum of bacteria and affects both Gram-positive and Gram-negative aerobic bacteria as well as some drug-resistant anaerobes. In addition, LVX is highly effective in treating unusual bacterial infections, such as non-gonococcal urethritis caused by Chlamydia trachomatis, Mycoplasma genitalium, Ureaplasma urealyticum, E. coli-induced diarrhea, Campylobacter jejuni and Shigella spp. (32).
E. coli resistance to lvx in the world. E. coli resistance to FQs was very low at approximately less than 2% in the 1990s; however, its resistance to LVX has significantly increased by more than 50% in 2000 (33). The resistance of some extended-spectrum beta-lactamase (ESBL)-producing microorganisms to LVX has reached 100%. In terms of geography, the reported prevalence rate of resistance to FQs varies among the European countries, from 7.9% in Sweden to 52% in Turkey. In the Asian countries, the prevalence rate of FQ-resistant E. coli in the samples of community-acquired UTI was reported to be about 25% in Korea (34) and 69% in India (35). In the United States, the frequency of LVX-resistant E. coli was 1% in 1994, but it varied from 2 to 27% among outpatients and inpatients with UTI in 2014 (36). It was reported that 23.4% of E. coli isolates in the Japanese population were resistant to LVX in 2012 (37 (38). Studies conducted on the antimicrobial resistance of E. coli in North American countries in addition to the high resistance of E. coli to LVX suggest that at least it would be preferable not to choose LVX as the first line of treatment in complicated UTIs (39).

E. coli resistance to FQs and lvx in Iran.
Many factors are involved in the induction of antibiotic resistance in E. coli (40), which are different in developed, developing, and underdeveloped countries (41).
Most of the studies in this field have been carried out in developed countries, so the comparison of bacterial resistance patterns to other countries, such as Iran, is relatively difficult (40 (44). In another Iranian report, the frequency of ESBL-producing E. coli isolates showed to be up to 89% (45). In other studies, resistance to LVX in UTI patients was 21.3-66.7% (44)(45)(46)(47)(48)(49)(50). Nonetheless, the proportion of ES-BL-producing isolates was determined in these studies. LVX resistance in E. coli isolates from patients with diarrhea is surprisingly low. For instance, it was 0% and 5.6% in non-ESBL-and ESBL-producing isolates, respectively (51)(52)(53). Two studies used more than one organ specimen (specimens from different body sites), and the rate of resistance to LVX was 43.8% and 61.6% in the hospitalized patients ( Fig. 1)  (54, 55).   The antimicrobial susceptibility of E. coli to FQs, especially LVX, has been more or less examined in Iran. Such studies indicate that E. coli strains isolated from UTI exhibit the highest rate of resistance to LVX among other samples. However, LVX resistance was different in various geographic regions of Iran. The antimicrobial resistance of E. coli to LVX was higher in the western provinces of Iran, such as Lorestan (46), Qazvin, Zanjan (47), and Kermanshah (44) than in the central ones, such as Tehran, Alborz, and Semnan (54,55), as well as in the southern province of Fars (51,52). According to the study conducted in Yasuj, the center of Kohgiluyeh and Boyer-Ahmad Province, 50 (34.7%) of 144 urine samples showed E. coli resistance to LVX (56). Four different studies conducted in the southern regions of Iran, i.e. Shiraz and Estahban) (48,(50)(51)(52), reported the antimicrobial resistance of E. coli isolates to LVX at 5.56 to 47.9%, while it was much higher (42.9-66.7%) in the western regions (44,46,47). One of the major points of present study was the significant difference in the resistance rate of E. coli isolated from inpatients and outpatients (Table 1). Therefore, one could conclude that the pattern of resistance to LVX in hospitalized and community-acquired patients did not significantly change from 2000 to 2015. The inappropriate administration, excessive prescription, and prescription of LVX without the antibiogram algorithm could be the reasons for not observing a difference between E. coli isolates from inpatients and outpatients in the Iranian health system. A study has been conducted in Tehran (the capital of Iran) in different periods of time, which have reported the pattern of E. coli resistance to LVX. According to this study, antimicrobial resistance to LVX has fluctuated between 33.3% and 100% during 2013 to 2018 (55).
In addition, data from other geographical regions of Iran indicate that LVX resistance has been following an ascendant pattern.
To sum it up, few studies have been conducted in Iran on E. coli resistance to FQs, especially LVX. Many studies have reported that the level of E. coli resistance to LVX in the western part of Iran has been increasing like many other countries in the world (44,46,47). The main reasons for the high prevalence of such resistance could be (a) the use of antibiotics in livestock, (b) the conditions of animal husbandry with livestock being common in the western region of Iran, (c) the local resistance pattern, (d) the duration of antibiotics consumption, (e) excessive prescription of antibiotics, (f) self-medication, (g) low health standards, (h) old age, (i) use of LVX for 48 hours during the last year (57). Indeed, to obtain a clearer view of the local pattern of E. coli resistance to LVX, further studies are required with different samples in different geographic regions of Iran to obtain comprehensive and accurate information about E. coli resistance to FQs, especially LVX.

CONClUsION
It is worth saying that all aforementioned studies have been carried out on samples collected from out-patients and inpatients in different regions. Therefore, it is difficult to make a comparison among them. Most studies were conducted in a short period of time (one year) and in a limited geographical region. According to the literature, although LVX has not been used for a long time in Iran, the resistance of E. coli, as a nosocomial pathogen, has been increasingly high due to LVX overuse. Thus, more attention must be paid to employing stewardship antibiotics.

ACKNOWleDGemeNTs
We thank faculty members of Rafsanjan University of Medical Sciences for their kind cooperation.